Structural properties and adsorption performance relationship towards three categories of lignin and their derived biochar.

• Lignin chemical structure affect the adsorption properties of lignin carbon. • Increased aromatic carbon improves the adsorption of methylene blue by lignin-derived carbon. • Pore adsorption can significantly affect the adsorption properties of lignin-derived carbon. • The maximum adsorption capacity of lignin-derived carbon for methylene blue was 526.32 mg/g. • After 6 cycles, lignin-derived carbon still removed 95.04% of methylene blue. The growing interest in utilizing lignin for dye removal has gained momentum, but there is limited information on the intricate relationship between lignin structural characteristics and adsorption efficacy, especially for its biochar derivatives. This study focused on three types of lignin and their corresponding biochar derivatives. Among them, ZnCl 2 -activated acidic/alkali densified lignin preparation of lignin-derived active carbon exhibited superior adsorption performance, achieving 526.32 mg/g for methylene blue and 2156.77 mg/g for congo red. Its exceptional adsorption capacity was attributed to its unique structural properties, including low alkyl and O-alkyl group content and high aromatic carbon levels. Furthermore, the adsorption mechanisms adhered to pseudo-second-order kinetics and the Langmuir model, signifying a spontaneous process. Intriguingly, lignin-derived active carbon also demonstrated remarkable recovery capabilities. These findings provide valuable insights into the impact of structural attributes on lignin and its biochar's adsorption performance. [ABSTRACT FROM AUTHOR]